The present invention generally relates to a dielectric film forming apparatus and a method for forming a dielectric film.
Currently, a piezoelectric element using a ferroelectric material (such as, lead zirconate titanate (Pb(Zr, Ti)O3, PZT) or the like) is applied to MEMS (a micro electro mechanical systems) technique (such as, an inkjet head and an acceleration sensor).
FIG. 4 is a graph showing piezoelectric characteristics of a PZT thin film having a (100)/(001) orientation and a PZT thin film having a (111) orientation. The PZT thin film having (100)/(001) orientation is known to show a piezoelectric characteristic greater than the piezoelectric characteristic of the PZT thin film with the (111) orientation.
FIG. 6 is an internal configuration diagram of a conventional dielectric film forming apparatus 110.
The dielectric film forming apparatus 110 includes a vacuum chamber 111, a target 121 for PZT provided in the vacuum chamber 111, a substrate holding pedestal 132 for holding a substrate 131 provided on a position facing to the target 121, a substrate heating portion 118 for heating the substrate 131, a sputtering power supply 113 applying electric voltage to the target, a sputtering gas introduction unit 114 for introducing sputter gas into the vacuum chamber 111, and first and second deposition preventive plates 134 and 135 provided in the vacuum chamber where particles discharged from the target 121 have adhered to.
In a case where a piezoelectric element is formed, a Si substrate having a thermally-oxidized film on which a Ti thin film as an adhesive layer and a noble metal thin film as a lower electrode layer are preliminarily laminated in this order is used as the substrate 131 to be film-formed. The noble metal thin film is a Pt or Ir thin film preferentially oriented to a (111) plane.
The substrate heating portion 118 includes a heat generating member 133 and a heating power supply 117. The heat generating member 133 is disposed at the opposite side of the substrate 131 on the substrate holding pedestal 132. The heating power supply 117 is electrically connected to the heat generating member 133.
When a direct current flows from the heating power supply 117 to the heat generating member 133, the heat generating member 133 generates heat and then the substrate 131 on the substrate holding pedestal 132 is heated.
FIG. 7 shows a temperature change of the heat generating member 133 in a film forming method using the conventional dielectric film forming apparatus 110.
First, the heat generating member 133 is heated to be a film forming temperature of 640 degrees Celsius and hold the temperature.
A cathode electrode 122 is closely adhered to and fixed onto the back side of the target 121 at the opposite side of the substrate holding pedestal 132. The sputtering power supply 113 is electrically connected to the cathode electrode 122.
Sputtering gas is introduced into the vacuum chamber 111 from the sputtering gas introduction unit 114; and an AC voltage is applied to the target 121 through the cathode electrode 122 from the sputtering power supply 113, the introduced sputtering gas being ionized so as to form plasma. Ions in the plasma sputter a surface of the target 121; and PZT particles are discharged from the target 121.
A part of PZT particles discharged from the target 121 enters a surface of the heated substrate 131; thus, a PZT thin film is formed on the noble metal thin film of the substrate 131.
After the PZT thin film having a predetermined film thickness is formed, the voltage applied from the sputtering power supply 113 is stopped and introduction of the sputtering gas is halted. The temperature of heat generating member 133 is lowered to 400 degrees Celsius that is a temperature lower than the temperature of during the film formation, and then, the film formation step is completed.
FIG. 8 shows X-ray diffraction patterns of three portions of the center portion (Center), the edge portion (Edge), and the middle portion (Middle) between the center portion and the edge portion in a PZT thin film formed on a Pt thin film using the conventional dielectric film forming apparatus 110. It is to be understood that the PZT thin film to be formed is preferentially oriented in a (111) direction.
In other words, in the conventional dielectric film forming apparatus, there has been a problem in that it is difficult to form a dielectric film having a (100)/(001) orientation. See examples such as, JPA No. 2007-327106, JPA No. 2010-084180 and JPA No. 2003-081694.